There is an increasing necessity of removing, from exhaust gases, particulates and toxic substances in the exhaust gases of an internal combustion engine, a boiler and the like in consideration of influences on environments. Especially, regulations concerning removal of the particulates (hereinafter referred to as the “PM” in some case) discharged from a diesel engine tend to be globally tightened. Attentions are paid to use of a filter (a honeycomb filter) constituted of a honeycomb structure as a trapping filter (a diesel particulate filter, hereinafter referred to as the “DPF” in some case) for removing the PM, and various systems are proposed. The above DPF has a structure in which a plurality of cells constituting channels of a fluid are usually defined by porous partition walls. Since the cells are alternately plugged, the porous partition walls constituting the cells perform a function of the filter. As a material of the DPF, a cordierite is preferably used because it has a low coefficient of thermal expansion and a high resistance to thermal shock.
Such a cordierite-based honeycomb structure is manufactured by, for example, obtaining a clay by use of a cordierite forming material including an alumina source material which is an alumina source; extruding the resultant clay into a honeycomb shape to obtain a formed honeycomb body in which a plurality of cells are defined by the partition walls; drying the resultant formed honeycomb body to obtain a dried honeycomb body; and firing the resultant dried honeycomb body (e.g., Patent Document 1).
The honeycomb filter using the honeycomb structure manufactured in this manner is attached to an exhaust gas system of the diesel engine when used. Therefore, reduction of a pressure loss of the filter is demanded so that a performance of the engine can sufficiently be exerted.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-40687